What is Latitude? - Definition, Calculation & Examples

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• 0:01 Definition of Latitude
• 1:45 Calculation of Latitude
• 4:20 Lesson Summary

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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

In this lesson, you will learn what latitude is and the general principles behind how it can be calculated. You'll also be provided with some examples of latitudes around the world. A short quiz will follow.

Definition of Latitude

People have known the Earth was round for a long time, far earlier than Christopher Columbus. Perhaps everyday people did not know the shape of the Earth, but the navigators aboard tall ships certainly did. Without this knowledge navigation would have been impossible, and every ship would have gotten lost. Part of the reason for this is the effect of latitude.

Latitude and longitude are two coordinates that, together, tell you exactly where you are on the Earth. Latitude tells you where you are between the North Pole and the South Pole. The equator is zero degrees, the North Pole is 90 degrees North, and the South Pole is 90 degrees South, and in between is in between.

Parallels, otherwise known as latitude lines, are lines that run across the Earth from east to west at a constant latitude. Everywhere on a parallel must have the same latitude. An example would be the equator, which is at zero degrees of latitude.

Other important parallels include the Tropic of Cancer (at 23.4 degrees North), the Tropic of Capricorn (at 23.4 degrees South), the Arctic Circle (at 66.5 at degrees North), and the Antarctic Circle (at 66.5 degrees South). And here are a few other examples: Houston, Texas, is at 30 degrees North; whereas Manchester, England, is 53.4 degrees North; and Oulu, Finland, is 60 degrees North. Wellington, New Zealand, on the other hand, is 41 degrees South.

Latitude is important for navigation because the path of the sun is different depending on your latitude. It also varies based on the time of year, so the whole thing is very complicated! Navigators would have had to really know what they were doing to navigate by the sun and the stars.

Calculation of Latitude

The full calculation of latitude is quite involved, so we'll go through some of the basic principles. Let's say that today is the equinox, meaning that day and night are exactly the same length. Another way of putting it is that the equator points directly at the sun - the Earth isn't tilting towards or away from the sun.

If you live at the equator, the sun will pass directly overhead on this day. It will rise in the East and set in the West, and be overhead in the middle of the day. If you live south of the equator, it will arch across the Northern sky, still rising in the East and setting in the West - its path is just an arc to the north. If you live north of the equator, it will arc across the Southern sky, though still rising in the East and setting in the West - its path is just an arc to the south. This makes sense because if it's directly overhead at the equator, and the equator is to your south, you should see the sun off to the south.

But, how far south? This is where latitude comes in. At the equator (zero degrees latitude) the sun is directly overhead in the middle of the day, and at the North Pole (90 degrees latitude) the sun would be right on the horizon to the south. So, it follows that your latitude tells you the angle of the sun in the sky.

Houston, Texas, has a latitude of approximately 30 degrees North. At the equator (zero degrees) the sun is directly overhead, so in Houston, the sun must be 30 degrees below being directly overhead. Or, in other words, it's 60 degrees above the Southern horizon (90 - 30 = 60).

So, if you know your latitude, you know the angle of the sun in the sky on the equinox. But the process works the other way, too. On the equinox, all you have to do to figure out your latitude is measure the angle of the sun, using either a vertical (directly above you) or a horizontal (straight in front of you) line of reference at the middle of the day. Easy!

Unfortunately, it's not always the equinox. To do this in real life you have to adjust for the fact that the Northern Hemisphere is tilted towards the sun during the Northern summer, and tilted away from the sun during the Northern winter. That throws your calculations off by a certain angle, but the basic principle of measuring the sun's angle is the same.

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